WO2006111757A2 - Animal model of vascular smooth muscle cell apoptosis - Google Patents

Abstract

This invention relates to non-human animal model which expresses a heterologous nucleic acid encoding a receptor for an apoptotic agent, such as diphtheria toxin (DT), specifically in Vascular Smooth Muscle Cells (VSMCs) of blood vessel walls. This allows apoptosis to be induced with very high specificity in these VSMCs and provides a useful model system for a range of vascular conditions, including angiogenesis, calcification and atherosclerosis.

Description

Animal Model of Vascular Smooth Muscle Cell Apoptosis

This invention relates to means, in particular non-human animal models, for the study of conditions associated with apoptosis in the vascular system, including vascular injury and atherosclerosis.

Vascular smooth muscle cells (VSMCs) together with their synthetic products, elastin, collagen, and extracellular matrix components, comprise the medial layer of adult arteries. In humans, VSMCs are also present in the intima, and intimal accumulation of VSMCs is a feature of both atherosclerosis and restenosis after vessel injury. Changes in VSMC number are determined by the net balance of VSMC proliferation, migration and cell death. VSMC proliferation rates are low in adult arteries, even in advanced atherosclerotic plaques, although transient proliferative responses occur after vessel injury ^1/2.

The role of VSMC death in vessel pathology is unclear.

Although VSMC death rates are low in adult vessels, increased death occurs as plaques develop ³ and massive medial VSMC apoptosis is seen after injury ⁴'⁵. Medial VSMC death is followed by proliferation of the remaining cells, such that normal tissue homeostasis is achieved several weeks post injury ^δ. This recovery indicates that medial VSMC number is tightly regulated. Chronic, low-level VSMC death is also a characteristic feature of arterial aneurysms where loss of medial VSMCs, accompanied by inflammation, fragmentation of elastin and matrix degradation, leads to progressive dilatation and potential rupture ⁷. In contrast, medial VSMC apoptosis accompanies negative remodelling (vessel shrinkage) in regression of vessels after birth or after changes in blood flow ⁸'⁹. In atherosclerosis, intimal VSMC apoptosis is increased in unstable versus stable lesions and has been implicated in the rupture of atherosclerotic plaques ¹⁰. In addition to the direct structural consequences of VSMC loss by cell death, VSMC apoptosis has also been suggested to provoke inflammation, to be pro-coagulant both locally and systemically, and to predispose to calcification.

Thus, VSMC apoptosis initiated by seeding genetically altered rat VSMCs induced expression of monocyte-chemoattractant protein-1 (MCP-I) and IL-8, causing massive infiltration of macrophages in vivo ¹¹. This inflammatory reaction is driven by caspase and calpain-mediated release of IL-lα,¹². VSMCs undergoing apoptosis express phosphatidylserine and act as a substrate for thrombin generation ¹³. In vivo, much of the pro- coagulant activity of the necrotic core of plaques is due to apoptotic cells ¹⁴, and systemic pro-coagulant activity has also been attributed to microparticles released from apoptotic cells ¹⁵. Finally, apoptotic VSMCs can initiate calcification by concentrating calcium and phosphate in apoptotic bodies ¹⁶.

Although a number of approaches have been employed to examine the role of VSMC apoptosis, including administration of agents to promote or block death, and the seeding of genetically manipulated cells that are induced to die, the contribution of VSMC apoptosis in isolation is still not clear because these approaches have produced controversial and contradictory findings ⁴¹'⁴². For example, some studies indicate that adenovirus-mediated expression of Fas-L or antisense oligonucleotides to Bcl-X_L inhibits neointimal formation after arterial injury ⁴¹'⁴², while other studies have found either no change in lumen size or an increase in neointima following VSMC apoptosis ¹⁷. Similarly, although some studies have found massive induction of apoptosis induces little inflammation ⁴¹'⁴², inflammation is the major effect observed in other studies ¹¹'¹⁷. These contradictory findings may be explained by the lack of cell-specificity of viral transfection, especially given that core pathways regulating cell death are highly conserved, and thus manipulation may induce death of many vascular cell types. Similarly, the seeding of in vitro manipulated cells into the lumen of a vessel to form a neointima is highly artificial, with administration resulting in vessel damage, and subsequent induction of VSMC death likely to produce different effects to that seen on death of medial VSMC within their native extracellular milieu.

The present inventors have developed a non-human animal model in which apoptosis can be induced with very high specificity in the VSMCs of blood vessel walls. This apoptosis is found to occur without inflammation or reactive cell division in the blood vessel and without any cellular loss or gross morphological changes in other tissues. This model system is useful, in particular for the long-term study of vascular injury, and the screening of drug candidates.

One aspect of the invention provides a transgenic non-human animal comprising a heterologous nucleic acid which encodes a receptor for an apoptotic agent, wherein said heterologous nucleic acid is expressed specifically in Vascular Smooth Muscle Cells (VSMCs) of said non-human animal .

A receptor for an apoptotic agent interacts with an apoptotic agent, such as an apoptotic polypeptide, to induce apoptosis of the cell expressing the receptor. For example, the interaction of a receptor encoded by the heterologous nucleic acid expressed by a VSMC with the apoptotic agent induces apoptosis in the VSMC. Interaction may include, for example, the receptor-mediated uptake of the apoptotic agent into the VSMC or the enzymatic activation of the apoptotic agent by conversion of a pro-drug. Thus, VSMC apoptosis may be specifically induced by the administration of the apoptotic agent to the non-human animal .

VSMC apoptosis induced by the interaction of the receptor and the apoptotic agent preferably occurs in blood vessels in the absence of reactive cell division or inflammation in the blood vessels .

Preferably, non-human animal cells which do not express the heterologous nucleic acid are unable to interact with the apoptotic agent i.e. the apoptotic agent does not induce apoptosis and has no effect on the cells of the non-human animal in the absence of expression of the receptor expressed by the heterologous nucleic acid. For example, the encoded receptor which interacts with the apoptotic agent may be heterologous and the receptors which are naturally expressed by the non-human animal (i.e. endogenous or homologous receptors) may not interact with the apoptotic agent.

In some preferred embodiments, the receptor is a Diphtheria toxin receptor (DTR) .

Diphtheria toxin (DT) binding to the Diphtheria toxin receptor (DTR) (also called heparin binding epidermal growth factor- like receptor: HB-EGF) on the surface of VSMCs initiates uptake of DT ¹⁹. Upon endocytosis, the DT A subunit catalyses ADP ribosylation of elongation factor 2, resulting in inhibition of protein synthesis ²⁰ and induction of apoptosis in both dividing and terminally differentiated cells. A 3- amino acid substitution in the extracellular region of rodent DTRs, for example, renders them unable to mediate endocytosis of DT ²¹'²². Thus, expression of a mammalian DTR that interacts with DT, such as human DTR (hDTR) , under the control of a cell type-specific promoter confers DT-uptake to specific non-human animal cells.

Any suitable mammalian DTR that interacts with DT and confers DT sensitivity on a cell may be used in accordance with the invention, including, for example, Canis Familiaris DTR (database entry XP_544289.1 GI: 57043431), Bos Taurus DTR (database entry XP_601210.1 GI: 61813227), Sus Scrofa DTR (database entry CAA75740.1 GI: 2654362), and primate DTRs, including monkey DTRs, such as Cercopithecus Aethiops (African green monkey) (database entry A41914 GI: 419995; Valdizan et al J Biol Chem 1995; 270:16879-85).

In preferred embodiments, the heterologous receptor is the human diphtheria toxin receptor (hDTR) (database accession number AY164533.1 GI: 24286764) or a variant or fragment thereof. hDTR is shown herein to be useful as a heterologous apoptotic agent receptor in non-human animals over long periods (e.g. months), which may be required for vascular work, with minimal if any toxicity, at appropriate doses.

A suitable apoptotic agent for inducing apoptosis in non-human animal VSMCs expressing the diphtheria toxin receptor is diphtheria toxin (DT: database accession number AY820132.1 GI: 56068038) or a variant or fragment thereof.

Suitable variants or fragments of hDTR and DT polypeptides retain the activity of the wild-type sequences to interact with DT or hDTR, respectively and mediate cell apoptosis. A variant may have one or more of addition, insertion, deletion or substitution of one or more amino acids in the wild-type polypeptide sequence. For example, up to about 5, 10, 15 or 20 amino acids may be altered. Such alterations may be caused by one or more of addition, insertion, deletion or substitution of one or more nucleotides in the encoding nucleic acid.

An amino acid sequence variant of a wild-type polypeptide sequence, may comprise an amino acid sequence which shares greater than 20% sequence identity with the wild-type sequence, greater than 30%, greater than 35%, greater than 40%, greater than 45%, greater than 55%, greater than 65%, greater than 70%, greater than about 80%, greater than 90% or greater than 95%. The sequence may share greater than 20% similarity with the wild-type sequence, greater than 30% similarity, greater than 40% similarity, greater than 50% similarity, greater than 60% similarity, greater than 70% similarity, greater than 80% similarity or greater than 90% similarity.

Sequence similarity and identity are commonly defined with reference to the algorithm GAP (Wisconsin GCG package,

Accelerys Inc, San Diego USA) . GAP uses the Needleman and Wunsch algorithm to align two complete sequences that maximizes the number of matches and minimizes the number of gaps. Generally, default parameters are used, with a gap creation penalty = 12 and gap extension penalty = 4. Use of GAP may be preferred but other algorithms may be used, e.g. BLAST (which uses the method of Altschul et al. (1990) J. MoI. Biol. 215: 405-410), FASTA (which uses the method of Pearson and Lipman (1988) PNAS USA 85: 2444-2448), or the Smith- Waterman algorithm (Smith and Waterman (1981) J. MoI Biol. 147: 195-197), or the TBLASTN program, of Altschul et al. (1990) supra, generally employing default parameters. In . particular, the psi-Blast algorithm (Nucl. Acids Res. (1997) 25 3389-3402) may be used. Sequence identity and similarity may also be determined using Genomequest™ software (Gene-IT, Worcester MA USA) .

Sequence comparisons are preferably made over the full-length of the relevant sequence described herein.

Similarity allows for "conservative variation", i.e. substitution of one hydrophobic residue such as isoleucine, valine, leucine or methionine for another or the substitution of one polar residue for another, such as arginine for lysine, glutamic for aspartic acid, or glutamine for asparagine.

Preferably, the heterologous nucleic acid is expressed in VSMCs but not in other cell-types or tissue within the non- human animal, in particular smooth muscle cells in other tissue, such as the gut. Apoptosis induced by the interaction of the receptor and the apoptotic agent preferably occurs specifically in the vascular system of the non-human animal. A heterologous nucleic acid is a nucleic acid that is outside its natural environment i.e. it is not naturally occurring within the non-human animal. The heterologous nucleic acid may, for example, have been introduced into the non-human animal or an ancestor thereof by recombinant techniques (i.e. it may be a recombinant nucleic acid) .

The heterologous nucleic acid may be comprised in a construct or vector. Suitable vectors can be chosen or constructed, containing appropriate regulatory sequences, including promoter sequences, terminator fragments, polyadenylation sequences, enhancer sequences, marker genes and other sequences as appropriate. In preferred embodiments, the vector comprises a positive or negative selectable marker, for example an antibiotic resistance or sensitivity gene, which may be used in identifying transformants which contain the heterologous nucleic acid, as is well known in the art.

Vectors may be plasmids, viral e.g. 'phage, or phagemid, as appropriate. For further details see, for example, Molecular Cloning: a Laboratory Manual: 3rd edition, Russell et al . , 2001, Cold Spring Harbor Laboratory Press. Many known techniques and protocols for manipulation of nucleic acid, for example in preparation of nucleic acid constructs, mutagenesis, sequencing, introduction of DNA into cells and 'gene expression, and analysis of proteins, are described in detail in Current Protocols in Molecular Biology, Ausubel et al. eds., John Wiley & Sons, 1992.

The heterologous nucleic acid may be operably linked to a VSMC specific regulatory element. The VSMC specific regulatory element is preferably not an element with which the nucleic acid encoding the receptor is associated in nature (i.e. the element is heterologous to the nucleic acid) . Suitable VSMC specific regulatory elements include the SM22 alpha (Imai T et al. Circ Res. 2001; 89 : 55-62.) , smooth muscle cell actin (Mack CP et al Circ Res. 1999; 84 : 852-861) , smooth muscle myosin heavy chain (Zilberman A, et al Circ Res. 1998; 82 : 566-575) and smoothelin (Rensen SS et al Cardiovasc Res. 2002;55:850-863) promoters.

The data herein shows that the effects of SM22α gene promoter expression are highly vascular-specific in adult non-human animals. In some preferred embodiments, a suitable VSMC specific regulatory element may comprise or consist of a SM22α promoter, in particular a rodent SM22α promoter such as a murine or rat SM22α promoter.

The Rattus Norvegicus (rat) SM22 alpha promoter is contained in the database entry Z48607.1 GI: 728638. The Mus musculus (mouse) SM22 alpha promoter is contained in database entry U36589.1 GI: 1330322.

An SM22α promoter preferably comprises or consists of the nucleotide sequence of residues -445 to +88 relative to the transcriptional start site of the murine SM22α gene sequence (Regan CP et al J Clin Invest. 2000; 106:1139-1147) or may be a variant thereof.

Suitable variants of the SM22α promoter sequence retain the activity of the wild-type sequence to direct VSMC specific expression of linked genes. A variant may have one or more of addition, insertion, deletion or substitution of one or more nucleotides in the wild-type nucleotide sequence. For example, up to about 10, 20, 50 or 100 nucleotides may be altered.

A nucleotide sequence variant of a wild-type sequence, may comprise a nucleotide sequence which shares greater than 20% sequence identity with the wild-type sequence, greater than 30%, greater than 35%, greater than 40%, greater than 45%, greater than 55%, greater than 65%, greater than 70%, greater than about 80%, greater than 90% or greater than 95%.

Administration of the apoptotic agent to the non-human may be by any suitable means to achieve apoptosis of VSMCs expressing the receptor. Conveniently, the apoptotic agent is parenterally administered, for example, by injection, in particular intraperitoneal injection. Any dosage regimen suitable to achieve VSMC apoptosis may be employed, for example lng/g to 15 ng/g body weight may be employed.

Non-human animals in which VSMC apoptosis can be induced in the vascular system by the administration of an apoptotic agent are useful as models for a range of vascular conditions.

Vascular conditions include vascular damage or injury, which may include physical, radiation or chemical damage (for example, damage caused by angioplasty or stent implantion, brachytherapy or phototherapy) , aneurysm formation, proliferative vascular diseases including diabetic retinopathy, angiogenesis including tumour or diabetic angiogenesis, vasculogenesis (including general development of other tissues), calcification, hypertension, vascular remodeling, congenital heart disease (including supravalvar aortic stenosis), medial atrophy (for example, in atherosclerosis) , vein or other graft implantation, neointima formation, vein graft disease, or accelerated vascular disease associated with rejection of transplanted organs.

In some embodiments, the non-human animal which comprises the heterologous nucleic acid may have increased susceptibility to atherosclerosis relative to controls. An animal with increased susceptibility to atherosclerosis may be produced by recombinant techniques, for example by the mutation or knock- out of one or more components of lipid metabolism in the animal. Various non-human animals with increased susceptibility to athrosclerosis are known in the art and include animals deficient in Apolipoprotein E (ApoE) and/or LDL receptor.

A transgenic non-human animal which comprises a heterologous nucleic acid encoding a receptor for an apoptotic polypeptide, wherein said heterologous nucleic acid is expressed specifically in Vascular Smooth Muscle Cells (VSMCs) , may be ApoE deficient and/or LDL receptor deficient.

In some embodiments, the non-human animal may be ApoE deficient i.e. the animal may have reduced levels of expression or activity of ApoE. ApoE is a constituent of VLDL particles and plays an important role in cholesterol and fatty acid metabolism. Non-human animal ApoE protein and nucleic acid sequences are well known in the art. For example, mouse ApoE has the sequence of database entry NP_033826.1 GI: 6753102 and rat ApoE has the sequence of database entry AAH86581.1 GI: 55824759. Examples of ApoE deficient animals include APOE*3 Leiden 1 mutants (Groot PH et al Arterioscler Thromb Vase Biol. 1996; 16:926-933).

In some embodiments, the non-human animal may be LDL receptor deficient i.e. the animal may have reduced levels of expression or activity of LDL receptor. The LDL receptor mediates the uptake of lipid-carrying lipoprotein particles, such as LDL, into cells. Non-human animal LDL receptor protein and nucleic acid sequences are well known in the art. For example, the mouse LDL receptor coding sequence has the database entry NM_010700.1 GI: 6754525 and rat LDL receptor coding sequence has the database entry NM_175762.2 GI:31343479.

A transgenic non-human animal that is deficient in a lipid metabolism polypeptide such as ApoE or LDL receptor may have reduced or abrogated levels or activity of the polypeptide. For example, the non-human animal may comprise a mutation in the coding sequence or its regulatory elements that reduce or abrogate the expression or activity of the lipid metabolism polypeptide. Suitable mutations include insertions, deletions, substitutions or frameshifts. A non-human animal deficient in a lipid metabolism polypeptide may be heterozygous or, more preferably, homozygous for mutation in the gene encoding the lipid metabolism polypeptide. Methods and means of producing non-human animals with are deficient in a lipid metabolism polypeptide, including, for example ApoE deficient animals, such as ApoE knockouts, are well-known in the art and are described for example in Johnson et al

Atherosclerosis (2001) 154 399-406, Zhang, S. H. et al . Science 258, 468-71 (1992), Piedrahita, J.A. et al Proc Natl Acad Sci U S A 89, 4471-5 (1992) .

Non-human animals deficient in a lipid metabolism polypeptide such as ApoE or LDL receptor, are susceptible to atherosclerosis and are prone to accumulate atherosclerotic plaques in their blood vessels, in particular when fed on a high fat diet. Induction of VSMC apoptosis in non-human animals which have increased atherosclerosis susceptibility induces many features which are characteristic of advanced human atherosclerotic lesions, such as inflammation and medial atrophy. VSMC apoptosis may also induce the rupture of plaques and sudden death. Non-human animals as described herein may be useful as models for atherosclerosis and related conditions, in particular, for studying development of plaques susceptible to rupture and plaque rupture itself. A non-human animal may be fed on a high fat diet to promote accumulate atherosclerotic plaques in the blood vessels.

In non-human animals deficient in a lipid metabolism polypeptide such as ApoE or LDL receptor, which are susceptible to atherosclerosis, the heterologous nucleic acid encoding the receptor for the apoptotic agent is preferably operably linked to an SM22α promoter, which is shown herein to be active in atherosclerotic plaques. Suitable SM22α promoters are described in more detail above. Suitable non-human animals for use in accordance with all aspects of the present invention include rodents such as rats and mice and other useful models of human disease such as pigs.

A method of producing a transgenic non-human animal as described herein may comprise: introducing a heterologous nucleic acid encoding a receptor for an apoptotic agent operably linked to a VSMC specific regulatory element into a non-human animal germ line cell, and; generating a transgenic non-human animal from said non- human animal germ line cell.

The heterologous nucleic acid encoding the receptor may be operably linked to suitable regulatory elements and may be comprised in a vector as described above.

A suitable non-human animal germ-line cell may include an egg, oocyte or embryonic stem (ES) cell. In some embodiments, the nucleic acid may be introduced into a germ line cell that is comprised in an early stage embryo, such as a blastocyst.

The heterologous nucleic acid or vector may be introduced into the germ line cell using any method known in the art, including, for example, pronuclear microinjection; retrovirus mediated gene transfer into germ lines; gene targeting in embryonic stem cells; electroporation of embryos; sperm- mediated gene transfer; and calcium phosphate/DNA co- precipitates, microinjection of DNA into the nucleus, bacterial protoplast fusion with intact cells, transfection, polycations, e.g., polybrene, polyornithine, etc., (See, for example Van der Putten, et al., 1985, Proc. Natl. Acad. Sci., USA 82:6148-6152; Thompson, et al., 1989, Cell 56:313-321; Lo, 1983, MoI Cell. Biol. 3:1803-1814; Lavitrano, et al . , 1989, Cell, 57:717-723 Gordon, 1989, Intl. Rev. Cytol . , 115:171-229; Keown et al . , 1989, Methods in Enzymology; Keown et al . , 1990, Methods and Enzymology, Vol. 185, pp. 527-537; Mansour et al . , 1988, Nature, 336:348-352).

After the heterologous nucleic acid or vector has been introduced into cells, the cells in which the heterologous nucleic acid has successfully incorporated into the non-human animal germ-line cell genome may be identified.

Cells comprising the heterologous nucleic acid may be identified, for example, by detecting the expression of a marker gene. For example, transformed cells may be treated with a selective agent that selects either cells expressing or cells not expressing the selectable marker. Many suitable selectable markers and agents are known in the art. For example, cells that express the introduced neomycin resistance gene are resistant to the compound G418, while cells that do not express the neo gene marker are killed by G418.

Successful insertion of the heterologous nucleic acid into the genome may be confirmed by analyzing the DNA of the selected cells using routine techniques, such as PCR and/or Southern analysis .

A non-human animal may be generated from a cell comprising the heterologous nucleic acid or vector using standard techniques (see for example Piedrahita et al (1992) PNAS USA 89 4471- 4475, Roller et al (1989) PNAS USA 86 8927-8931; Transgenic Animal Technology: A Laboratory Handbook, Pinkert CA (2002) Academic Press)

For example, the cell may be introduced into a blastocyst. The injection of transformed cells injected into a non-human animal blastocyst may lead to the formation of chimeras (see e.g., Bradley, A. in Teratocarcinomas and Embryonic Stem Cells: A Practical Approach, E. J. Robertson, ed., IRL, Oxford, pp. 113-152 (1987)). Alternatively, germ-line cells identified as comprising the heterologous nucleic acid may be allowed to aggregate with dissociated mouse embryo cells to form the aggregation chimera, A chimeric embryo can then be implanted into a suitable pseudopregnant female foster non- human animal and the embryo brought to term. Chimeric progeny harbouring the heterologous nucleic acid in their germ cells can be used to breed non-human animals in which all cells of the non-human animal comprise the heterologous nucleic acid.

Non-human animals produced as described may be crossed with non-human animals of the same or other genotypes to produce descendents. For example, the non-human animal or descendent may be crossed with a non-human animal which is deficient in a lipid metabolism polypeptide such as ApoE or LDL receptor, to produce offspring that are susceptible to atherosclerosis and specifically express the heterologous nucleic acid in VSMCs.

The genotype of the non-human animal or descendent may be determined. A method may include determining that the non- human animal or the descendent specifically expresses the heterologous nucleic acid encoding the receptor in VSMCs. Methods of determining the genotype of a non-human animal are well-known in the art.

Other aspects of the invention relate to the use of non-human animals as described above in the screening and identification of compounds which may be useful in treating vascular conditions .

A method of screening for a compound useful in the treatment of a vascular condition, including vascular damage or injury, may, for example, comprise; administering a test compound to a transgenic non-human animal which specifically expresses a heterologous nucleic acid encoding a receptor for an apoptotic agent in Vascular

Smooth Muscle Cells (VSMCs) of the non-human animal, administering the apoptotic agent to said non-human animal, and; determining the effect of said apoptotic agent in the presence of the test compound.

Administration of the apoptotic agent induces apoptosis in cells expressing the heterologous nucleic acid. Preferably, the apoptotic agent does not interact with or induce apoptosis in cells which do not express the heterologous nucleic acid.

Reduced apoptotic effects in the presence relative to the absence of test compound may be indicative that the compound is useful in the treatment of a vascular condition.

Vascular conditions include vascular damage or injury, which may include physical, radiation or chemical damage (for example, damage caused by angioplasty or stent implantion, brachytherapy or phototherapy) , aneurysm formation, proliferative vascular diseases including diabetic retinopathy, angiogenesis including tumour or diabetic angiogenesis, vasculogenesis (including general development of other tissues) , calcification, hypertension, vascular remodeling, congenital heart disease (including supravalvar aortic stenosis) , and medial atrophy (for example, in atherosclerosis) , vein or other graft implantation, neointima formation, vein graft disease, or accelerated vascular disease associated with rejection of transplanted organs.

The effect of the test compound on the frequency of VSMC apoptosis which is induced by the apoptotic polypeptide may be determined. For example, the proportion or percentage of VSMC cells which are apoptotic may be determined. This may be performed by detecting the presence or absence of standard markers for apoptosis in VSMCs.

The effect of the test compound on the cellular consequences of VSMC apoptosis may be determined. This may be achieved by determining the presence or extent of markers of plaque rupture in the non-human animal . Markers of plaque rupture may include discontinuity of fibrous cap, intraplaque haemorrhage and thrombus extending into the lumen.

The effect of the test compound on the clinical symptoms of VSMC apoptosis may be determined. This may be achieved by determining the presence or extent of symptoms in the non- human animal. Markers of plaque rupture may include heart attack, death and stoke.

A method of screening for a compound useful in the treatment of atherosclerosis may comprise; administering a test compound to a transgenic non-human animal which specifically expresses a heterologous receptor for the apoptotic agent in Vascular Smooth Muscle Cells (VSMCs) , wherein said non-human animal has increased susceptibility to atherosclerosis; administering the apoptotic agent to said non-human animal and. determining the effect of said polypeptide in the presence of the test compound.

Administration of the apoptotic agent induces apoptosis in

VSMCs expressing the heterologous receptor. Reduced apoptotic effects in the presence relative to the absence of test compound may be indicative that the compound is useful in the treatment of atherosclerosis.

The effect of the test compound on the frequency of VSMC apoptosis, cellular consequences of VSMC apoptosis and/or clinical symptoms of VSMC apoptosis may be determined as described above. A non-human animal which has increased susceptibility to atherosclerosis has an increased probability of suffering from atherosclerosis or atherosclerosis-associated conditions than control animals. The animal may be deficient in a polypeptide component of lipid metabolism, such as ApoE or LDL receptor, as described above.

Preferably, the formation of atherosclerotic plaques is induced in the vascular system of a non-human animal prior to administration of said polypeptide. The may be achieved, for example, by feeding the non-human animal on a fat-rich diet (e.g. 20% or more fat for 4 or more weeks) to generate said atherosclerotic plaques. Suitable fat rich diets include a high fat diet comprising 21% fat, low cholate, 0.05% cholesterol (Research Diets - Western Diet D12079B) .

A compound which is useful in the treatment of atherosclerosis may also useful in the treatment of a range of atherosclerosis associated disorders, including cardiovascular conditions such as ischaemic (coronary) heart disease, myocardial ischaemia (angina) , myocardial infarction, aneurysmal disease, atheromatous peripheral vascular disease, aortoiliac disease, chronic and critical lower limb ischaemia, visceral ischaemia, renal artery disease, cerebrovascular disease, stroke, atherosclerotic retinopathy, thrombosis and aberrant blood clotting and hypertension.

Transgenic non-human animals suitable for use in the present screening methods are described in more detail above.

The apoptotic polypeptide and test compound may be administered by any convenient method, for example injection, including intravenous, cutaneous, subcutaneous or intraperitoneal injection. A test compound suitable for use in a method described herein may be any compound or molecular entity, such as a small organic molecule, peptide or nucleic acid.

A method described herein may comprise identifying a test compound as useful in the treatment of atherosclerosis or a vascular condition, for example a condition associated with vascular injury. Following identification of a compound using a method described above, the compound may be isolated and/or synthesised.

The identified compound may be synthesised using conventional chemical synthesis methodologies. Methods for the development and optimisation of synthetic routes are well known to persons skilled in this field.

A compound identified using a method described herein may be assessed or investigated further using one or more secondary screens. For example the toxicology and/or biological effect of the compound may be determined in wild-type non-human animals .

Following performance of a method described herein, the non- human animal may be sacrificed or euthanized.

The compound may be modified to optimise its pharmaceutical properties. The modified compound may be tested using the methods described herein to see whether it has the target property, or to what extent it is exhibited. Modified compounds include mimetics of the lead compound. Further optimisation or modification can then be carried out to arrive at one or more final compounds for in vivo or clinical testing.

The test compound may be used in preparation, i.e. manufacture or formulation, of a composition such as a medicament, pharmaceutical composition or drug. These may be administered to individuals, e.g. for the treatment of a condition described herein. A method may comprise formulating the test compound or the modified test compound in a pharmaceutical composition with a pharmaceutically acceptable excipient, vehicle or carrier. Suitable acceptable excipients, vehicles and carriers are well-known in the art.

The term "pharmaceutically acceptable" as used herein pertains to compounds, materials, compositions, and/or dosage forms which are, within the scope of sound medical judgement, suitable for use in contact with the tissues of a subject (e.g., human) without excessive toxicity, irritation, allergic response, or other problem or complication, commensurate with a reasonable benefit/risk ratio. Each carrier, excipient, etc. must also be "acceptable" in the sense of being compatible with the other ingredients of the formulation.

Suitable carriers, excipients, etc. can be found in standard pharmaceutical texts, for example, Remington's Pharmaceutical Sciences, 18th edition, Mack Publishing Company, Easton, Pa., 1990.

Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure. All documents mentioned in this specification are incorporated herein by reference in their entirety.

Certain aspects and embodiments of the invention will now be illustrated by way of example and with reference to the figures and table described below.

Figure 1 shows the structure of the Sm22α-DTR construct. The cDNA for the hDTR-eGFP fusion protein is inserted between the minimal SM22α promoter and an SV40 polyadenylation sequence, with the transcription start point indicated by the extended arrow. Small arrows show the location of the oligonucleotide primers used for genotype and expression analysis.

Figure 2 shows that long-term administration of DT results in a significant reduction of VSMCs. Presented data represent mean number of VSMCs per unit area of wall ± S. D for Control (n = 5), 28 d. DT (n = 7), and 28 d. DT + 14 d respite (n = 5) . Difference between control and both ablated groups is significant (* p = < 0.001), whilst variation between both ablated groups is not significant (** p = 0.96).

Figure 3 shows that loss of VSMCs does not induce vessel remodelling. Data points of vessel lumen circumference versus total number of cells per section are displayed as a scatter plot for control mice (black triangles) , 28 d. DT ablated (grey squares), and 28 d. DT +14 d. respite (open circles). Ablated vessels contain fewer cells per given lumen circumference, and following a 14 d. respite from DT do not remodel to the control lumen: cell ratio. Outer lines represent the 95% confidence interval for trend lines.

Difference between control and either DT or DT respite group is significant (p = <0.001), whilst variation between DT and DT respite groups is not significant (p = >0.42) .

Figure 4 shows that ablated vessels generate pharmacological responses to U6619 which are indistinguishable from normal vessels. Graphs show % of tension generated with repeated exposure to potassium (left panels) and % maximal contractile response with increasing dose of U6619. Data are means, error bars represent SEMs.

Figure 5 shows that ablated vessels generate pharmacological responses to phenylephidrine which are indistinguishable from normal vessels. Graphs show % of tension generated with repeated exposure to potassium (left panels) and % maximal contractile response with increasing dose of phenylephidrine . Data are means, error bars represent SEMs Figure 6 shows that ablated vessels generate pharmacological responses to ET-I which are indistinguishable from normal vessels. Graphs show % of tension generated with repeated exposure to potassium (left panels) and % maximal contractile response with increasing dose of ET-I. Data are means, error bars represent SEMs.

Figure 7 show that ablated vessels generate pharmacological responses to KCl that are indistinguishable from normal vessels. Graphs show % of tension generated with repeated exposure to potassium (left panels) and % maximal contractile response with increasing dose of KCl. Data are means, error bars represent SEMs

Fiqure 8 shows concentration-response curves to agonists as shown for transgenic mice were injected with either saline (circles) or DT (squares) at 5ng/g for 28 days and aortic rings analysed for contractile responses in a wire myograph (b) .

Figure 9 shows normalised concentration response curves for transgenic mice as in figure 8 with wall tension per 103 cells Presented data represent mean ± SEMs of control (n=5) and ablated (n=8) .

Table 1 shows the characteristics of plaques in DT treated SM22α-hDTR/ApoE-/- or control ApoE-/- mice. SM22α-hDTR/ApoE-/- and ApoE-/- mice were fed a Western diet for 12 weeks and DT at 5ng/g administered for 3 weeks. Individual plaques were analysed for cellular and structural composition as indicated. Data represent mean ±SEM, except for inflammatory foci which represents total number of inflammatory foci seen per total numbers of plaques examined (n = 12 mice, both groups) . Materials and Methods

All materials were purchased from Sigma-Aldrich unless otherwise stated.

Generation of transgenic animals

The minimal murine SM22α promoter (-445 to +88) was introduced into the pEGFP-Nl vector (Clontech) upstream of the hDTR fused in frame with eGFP. DNA was prepared using the endotoxin-free MaxiPrep kit (Qiagen) and linearised. Pronuclear injection of the vector into oocytes, implantation, and generation of chimeric progenitors was undertaken by Eurogentec (Belgium) .

Genotyping and treatment of animals

Weaned pups were tail tipped (in accordance with local regulations) , genomic DNA extracted, and genotype determined by PCR using hDTR-GFP primers: Fwd (5'- TTC CAC TGG ATC TAC GGA CC - 3'), and Rev (5'- TGT CGG CCA TGA TAT AGA CG - 3' ) . Confirmation of genotype and assessment of transgene copy number was carried out by Southern-blotting, as described previously ⁵¹ using a dCTP ³²P (Amersham) labelled probe excised from the original construct with Eco Rl and Xba I (NEB) . Two initial hDTR-GFP positive FVB founders were backcrossed onto a C57/BL6 background, and maintained as heterozygous breeding colonies to provide negative littermate controls. To analyse gene expression whole aortas or washed small intestine were roughly chopped directly in RNA-Stat60 (Tel-Test Inc.), homogenised, and RNA extracted as indicated by the manufacturer. RNA was DNase treated (Promega) , and 0.5 μg total used in first strand synthesis with Poly-(dT) (Promega), RNasin (Promega) and ± SuperRT (HT-Biotech) . Equal volumes of cDNA were used as template for a 30 cycle PCR, with half the reaction analysed by agarose electrophoresis. β-Actin was used as a positive control using the primers: Fwd (5'-TGG AAT CCT GTG GCA TCC ATG AAA C - 3'), and Rev (5'- TAA AAC GCA GCT CAG TAA CAG TCC G - 3' ) , with only 1/10^th of the reaction loaded. Purified recombinant DT (Quadratech Diagnostics) was prepared in 0.9% saline / 0.2% BSA (low endotoxin), sterile filtered, and stored at -80°C until used. Experimental animals were weighed and injected intraperitoneally with DT (doses as indicated) thrice weekly for long-term treatment. SM22α-DTR mice were fully backcrossed with ApoE^-/- mice. For experimental studies, SM22α-DTR/ApoE^-/- mice were given a high fat diet comprising 21% fat, low cholate, 0.05% cholesterol (Research Diets - Western Diet D12079B).

Histology and Immυnohistochemistry Experimental animals were euthanased under a rising concentration of CO₂, and tissues perfused in situ with 10% neutral buffered formalin (NBF) , followed by removal and overnight (o/n) fixation. Washed tissues were embedded in paraffin blocks, cut to 5μm serial sections, deparaffinated and stained with Haematoxylin and Eosin, by standard methods. Antigen retrieval was achieved by boiling in citrate buffer (pH 6.0). Mac-3 antigen (M3/84; Pharmingen) was detected by- blocking in 5% rabbit serum/TBS, incubation in primary ( 1^ry) antibody (Ab) at 1:200 o/n; Ki-67 antigen (MIB-I; Dako) was blocked in 10% goat serum/TBS*, incubated in 1^ry Ab at 1:100 o/n; cleaved caspase-3 antigen (C92-605; Pharmingen) was blocked in 5% goat serum/PBS, incubated in 1^ry Ab at 1:100 o/n; Mcp-l/JE antigen (#AF-479-NA; R&D Systems) was blocked using Cell and Tissue Kit (R&D Systems), incubated in 1^ry Ab at 1:100 o/n. CD3 antigen (NCL-CD3-12; Novacastra) was blocked in 5% rabbit serum/TBS, incubated in 1^ry Ab at 1:100 o/n. All were stained with biotinylated 2^ry Abs and detected with ABC reagents (Vector Laboratories) . Elastic Laminae were stained using a modified Verhoeff' s van Giesson stain (Bio-Optica; #053812). Masson' s Trichrome staining was achieved with Accustain Kit (HT-15) . Images were captured using a BX51 microscope (Olympus), air cooled CCD camera (CoolSnap) and imaging and analysis software (Soft Imaging Systems) . Final overlaid images were prepared using Photoshop 7.0 (Adobe). Transmission electron microscopy- Arteries were perfused in situ with 2.5% glutaraldehyde (EM grade I) in 0.1 M sodium cacodylate buffer, removed, and subsequently fixed o/n. Fixative was removed with one wash of 0.1 M sodium cacodylate buffer, and processed through osmium tetroxide, lead citrate, araldite embedding and ultra thin sectioning (60nm). Samples were analysed on a Philips CM150 TEM.

In vitro pharmacology

Female mice (control and SM22αDTR, 25-36g) were killed by CO₂ inhalation and the aorta removed and cleaned of fat and connective tissue. For each animal four consecutive rings (1- 2mm long) were cut from the thoracic portion of the aorta and mounted for the measurement of isometric tension in a wire myograph (Linton Instrumentation) , maintained at 37°C containing oxygenated Krebs' solution. Aortic rings were automatically normalised and set to 90% of the internal circumference they would be if fully relaxed and under a transmural pressure of 100mmHg. Vessels were then challenged three times with high K⁺ Krebs' solution (95mM K⁺) at 15 min intervals and allowed to re-equilibrate for 60 min. Cumulative concentration-response curves were constructed to the vasoconstrictors endothelin-1 (ET-I, 10^-10-3x10^-7M; Peptide Institute), phenylephrine (10^-9-10^-5M) and U-46619 (10^-10-3x10-

⁶M) . Experiments were terminated by the addition of 95mM K⁺ and agonist responses were expressed as a percentage of the maximum response (%KC1) . Concentration-response curves were also constructed to KC1 (10^-4-3X10^-1M) with responses expressed as a percentage of the maximum response (%maximum) . Data were analysed using the iterative curve-fitting programme FigSys (Biosoft) to obtain pD₂ (negative logio of the concentration required to produce 50% of the maximum response) and E_max values. Data for control and ablated animals were compared using Student's two-tailed t-test, with significance set at 95%. Results

Generation and characterisation of SM22α-DTR mice Transgenic mice were generated, using the construct depicted in Fig. 1, whereby expression of a hDTR-eGFP fusion protein is directed by the minimal murine SM22α promoter (-445 to +88) . Mice were genotyped by PCR and Southern blotting, and two founder lines established. Although the data presented is from one the founder line ( '1059' ) , the second founder ('1087') gave essentially identical results. Expression of transgene mRNA (hDTR-eGFP) was detected by RT-PCR, was restricted to arteries and absent from small intestine. Expression of SM22α was confirmed in both normal and atherosclerotic mouse arteries by in situ RT-PCR, and was confined to VSMCs. Taken together these data indicate specific expression of the hDTR- eGFP transgene by the minimal SM22α promoter in VSMCs only.

SM22α-DTR mice are born with the expected Mendelian frequency, develop normally, and have normal reproductive function and life spans.

Administration of DT results in activation of caspase-3 within VSMCs

To determine whether the hDTR-eGFP fusion protein could confer DT-sensitivity to VSMCs in vivo, transgenic and littermate controls were injected with two doses of purified DT at 5 ng/g of body weight over 72 h. At the end of this period aortas, carotid and brachiocephalic arteries were examined for morphological features of apoptosis and the presence of cleaved caspase-3 by immunohistochemistry. The cleaved caspase-3 antibody recognises a 'cryptic' site between the long and short domains of the proenzyme, which is only exposed following correct processing to the fully active form. Cleaved caspase-3 was found within VSMCs throughout the arteries of transgenic animals only, and not in DT-treated wild type littermates. H&E staining revealed many VSMCs with highly compacted, dark-stained nuclei within vessels of DT-treated transgenic animals, which is consistent with apoptosis, and was not seen in controls. In keeping with the localisation of the hDTR-eGFP protein in transgenic mice, active caspase-3 and nuclear condensation was also detected in the thoracic and abdominal aorta, the aortic bifurcation, and the brachiocephalic artery of DT treated transgenic animals. Apoptotic nuclei and cleaved caspase 3 positive SMC were not seen in other SMC-containing tissues, such as bladder and gut. Furthermore, VSMCs isolated from SM22αDTR mice treated with DT in vitro displayed cell retraction and chromatin condensation with Hoechst/PI staining, and dynamic cell blebbing when viewed by time-lapse videomicroscopy, again providing indication of apoptotic death.

Long term administration of DT causes specific ablation of VSMCs, but does not induce inflammation To examine the effect of chronic VSMC death on VSMC number and vessel architecture, mice were injected with 5ng/g DT three times weekly for 28 days. Mice tolerated DT treatment well, with no mortality or significant weight loss during the experimental period. Vessel cellularity was quantified by nuclear counts and total vessel wall area (demarcated by the internal and external elastic lamina) , using computer-aided morphometry, and expressed as total number of cells per mm² of vessel wall. In untreated animals, the cells per mm² of vessel wall was relatively constant across all arteries examined (thoracic, abdominal, and bifurcation of aorta, and carotid and brachiocephalic arteries) at 4946 + 207 cells per mm² (Fig. 2). This provides indication that during normal development, VSMC cellularity in large arteries is governed by spatiomechanical determinants and reaches a defined level irrespective of vessel location. Chronic DT treatment resulted in a significant time-dependent loss of VSMCs (50-70%) at all locations examined (Fig. 2) resulting in marked reduction in cell number per area.

Morphologically ablated vessels contained fewer nuclei, but otherwise appeared identical to control vessels. In particular, endothelial cells were seen at the luminal surface and intact elastic laminae were observed. Similarly, there was no evidence of vessel wall dissection, aneurysm formation, thrombus or coagulation. At 28 days, the accumulated cellular debris seen early after DT treatment had disappeared by histological or ultrastructural analysis, providing indication of the rapid removal of apoptotic VSMCs. Examination of SMC number at other sites including small intestine and bladder showed no change in cellularity or evidence of cell death.

To examine whether chronic VSMC cell death directly induces inflammation, we examined DT-treated arteries for monocyte/macrophages or lymphocytes using immunohistochemistry for Mac-3 or CD3 respectively. No infiltration by monocytes/macrophages or dendritic cells was seen into either chronically ablated vessels, or into acute short-term treated vessels. Previous studies have indicated that apoptosis of VSMCs by FADD activation induces expression of proinflammatory cytokines, including MCP-I¹², a chemoattractant for monocyte/macrophages. In contrast to this no murine MCP- 1/JE could be detected in ablated vessels.

Loss of VSMCs does not induce compensatory proliferation _f or vessel remodelling

To determine whether VSMCs were able to repopulate the vessel media after DT treatment, mice were treated for 28 days with DT and allowed to recover for 14 days in the absence of DT (DT-respite) . Vessels from DT-respite mice reveal no evidence of VSMC re-population, as judged by both an increase in cellularity, and expression of the cell proliferation marker Ki-67. Importantly, no neointima was observed in DT-respite vessels. These data provide indication that VSMC death alone, particularly in the absence of endothelial injury, does not result in proliferation of the remaining medial VSMCs, and does not result in a neointima.

To exclude the possibility that proliferation was not observed simply because the remaining VSMCs were non-viable, we cultured aortic explants from DT treated and control mice. Explanted aorta from both control and DT treated mice produced an outgrowth of VSMCs, with cells from DT-treated vessels proliferating faster than controls. This observation is in agreement with recent data demonstrating that VSMCs in an SM22α knockout mouse proliferate faster than controls³¹, and provides indication that the cells remaining after DT treatment may be a subset of SM22α-negative VSMCs.

To examine whether VSMC apoptosis could regulate vessel circumference independent of blood flow, we examined vessel remodelling in control and DT-treated mice. A strong linear correlation (R² = 0.87, p<0.01) exists between the lumen circumference and the total number of VSMCs in control vessels at all locations examined (~600 cells per 2 mm) (Fig. 3) .

Although DT-treated vessels also displayed this correlation (R² = 0.76, p<0.01), far fewer cells were present per unit circumference (~200 cells per 2mm) . This ratio remained constant in DT-respite mice, consistent with a lack of repopulation. These data provide indication that induction of VSMC apoptosis alone does not instigate vessel remodelling, and that changes in other factors, such as flow and shear stress, may be involved. However, it should be noted that this does not rule out VSMC apoptosis as the mode of vessel restructuring during remodelling, simply that induction of cell death alone does not induce vessel remodelling.

Loss of VSMCs does not alter contractile responses of isolated vessels . The primary function of adult VSMCs is to generate the tensile force required to contract vessels, and conversely release force to relax vessels, thus maintaining and regulating blood pressure. We therefore examined both active and passive contractile properties of isolated control and DT-treated vessels. Mice were injected with 5ng/g DT for 28 days and blood pressure measured using tail cuffs prior to sacrifice. Aortas were harvested, cleaned of adventitia and aortic rings mounted onto a wire myograph. Following normalisation, no significant difference between the internal diameter (μm) and resting tension (mN/itim) of vessel rings from control and DT treated mice was seen (Figs 4 to 9) , thus supporting the histology demonstrating intact elastic laminae. We examined the maximum response to 4 separate vasoconstrictors acting via different mechanisms. Both U46619 (a thromboxane A2 mimetic and powerful vasoconstrictor) and phenylephrine potently contracted aortas from all animals with no significant difference in either pD₂ or E_max between control and ablated groups (Figs 4, 5, 8 & 9). In control aortas, Endothelin-1 (ET-I) was without effect; although small responses were obtained in three of the 7 DT treated mice, this was not significant (Figure 6) . Importantly, the concentration- response curves and absolute tensions developed to KCl were not different between the two groups (Figure 7) . Therefore, despite a 50-70% loss of medial VSMCs, passive stretch (internal diameter) , basal tension and receptor-dependent or independent contractility of vessels is maintained in DT- treated mice. Assuming all VSMCs present in the vessel wall actively contract, this estimates the force generated per cell to have increased by ~2 fold in DT treated vessels. In keeping with these data, no significant difference in resting blood pressure between control and DT-treated mice was detected, providing indication that a level of redundancy or compensation exists in vivo, enabling VSMC-depleted vessels to functionally contract.

VSMC apoptosis induces plaque rupture and death in SM22α- DTR/ApoE^-/- mice.

To examine the effects of VSMC apoptosis in atherosclerosis, we generated SM22α-hDTR/ApoE-/- mice, and fed a Western diet from 6w of age. 12w later, 5ng/g DT was administered thrice weekly and mice sacrificed 3 weeks later. Aortic root plaques were analysed for plaque composition and structure using immunohistochemistry and computer-aided planimetry (Table 1) . Apoptosis was evident underlying the fibrous cap and around the necrotic core of SM22α-hDTR/ApoE-/- mice. In contrast, apoptosis was seen only around necrotic cores in control mice. DT did not affect plaque size, but induced a marked change in plaque phenotype in the SM22α-hDTR/ApoE-/- mice. In control mice plaques contained a thick VSMC-rich fibrous cap with abundant collagen and matrix overlying small necrotic cores, where cell debris was confined. Macrophages were scattered throughout the lesions, including the media. Fibrous caps were markedly thinner in SM22α-hDTR/ApoE-/- mice, with fewer cap VSMCs per plaque area and a smaller cap area per given plaque area (Table 1) . Cap cellularity (cells/area) was maintained indicating that both cells and extracellular matrix were reduced. Rupture of fibrous caps was seen where adjacent plaques coalesced. DT treatment of the SM22α-hDTR/ApoE-/- mice also markedly reduced collagen and matrix content in the plaque, with a larger percentage of the lesion occupied by necrotic cores (Table 1) . In addition, intense, localised macrophage accumulation and extensive apoptotic cellular debris was present within fibrous caps. These appearances are all features of advanced atherosclerosis, with fibrous cap thinning, loss of matrix, inflammation and VSMC apoptosis typical of vulnerable human plaques prone to rupture. These features were not confined to the aortic root - similar fibrous cap thinning was evident in brachiocephalic lesions, the earliest site of plaque development in these mice.

The data herein shows that selective induction of apoptosis in medial VSMCs, in the absence of other manipulations or pathological processes, is a silent phenomenon. Apoptosis alone is not sufficient to account for vessel repopulation, intima formation, aneurysm formation, inflammation, remodelling, thrombosis or calcification. Arteries can function normally despite massive cell loss, retaining both passive and active mechanical properties. This lack of sequelae may be due to the selective nature of the DT system for inducing single cell type specific death, and also the highly efficient clearance of apoptotic cells in vivo. In contrast, induction of VSMC apoptosis within stable lesions induces thinning of fibrous caps, inflammation, medial atrophy and intraplaque haemorrhage, suggestive of plaque rupture, all typical features of vulnerable plaques within advanced human atherosclerotic lesions. Chronic low level DT administration for 2-3 months was found to induce the same morphology of plaque vulnerability as a short term (2-3 w) treatment, and this effect was also seen in the brachiocephalic arteries (another vascular bed, widely considered to be the earliest and most advanced plaque in these mice) . Thus, transgenic animals as described herein may represent a valuable novel model of inducible plaque rupture.

Vascular calcification is a prominent feature of end stage renal disease (Goodman WG et al Am J Kidney Dis .2004; 43 (3) : 572-579), manifesting as intimal calcification in atherosclerotic plaques and also medial calcification of large elastic arteries and arterioles throughout the vascular tree (Goodman WG. J Nephrol .2002; 15 Suppl 6:S82-85). Calcification at either site is associated with an increased risk of myocardial infarction (Lehto S et al Arterioscler Thromb Vase Biol.1996; 16 (8 ): 978-983) . VSMC apoptosis promotes calcification of VSMCs, potentially leading to vascular calcification (Proudfoot D et al Circ Res.2000; 87(11) :1055- 1062) . Furthermore, chronic administration of DT to SM22α-

DTR/ApoE-/- has been found as described herein to induce both more frequent and extensive vascular calcification in plaques.. The transgenic animals described herein may therefore represent valuable model of vascular calcification, either alone or when crossed with other genetically modified mice, to study the mechanism of vascular disease associated with renal failure.

Physiological remodelling occurs in vascular development, such as closure of the ductus arteriosus due to the reduction in blood flow (Slomp J et al Arterioscler Thromb Vase Biol.1997; 17 (5) :1003-1009) , and reduction in lumen size of infra- umbilical arteries after birth (Cho A et al Circ Res.1995; 76:168-175). Surgical reduction in flow also results in compensatory reduction in VSMC numbers by apoptosis (Cho A et al Circ Res .1997; 81 (3) : 328-337; Kumar A et al Arterioscler Thromb Vase Biol .1997; 17 (10) : 2238-2244) . A further example of vessel remodelling accompanied by VSMC apoptosis comes from studies examining both development and regression of vessel hypertrophy/hyperplasia in hypertension. Hypertension is associated with VSMC apoptosis in cells from spontaneously hypertensive rats (Vega F et al American Journal of

Hypertension.1999; 12 (8 PtI) : 815-820) and in these rats as hypertension develops (Hamet P et al Hypertension.1995; 26: 642- 648; Sharifi AM et al American Journal of Hypertension 1998;11 (9) :1108-1116) . In addition, relief of either systemic or pulmonary hypertension results in apoptosis of VSMCs in the affected artery, with evidence that some antihypertensives are more potent than others (deBlois D et al Hypertension. 1997 29 (1 Pt2) : 340-349; Cowan KN et al Molecular Biology Of the Cell.1997 8 (Ss) : 1661-1661) . In particular, angiotensin converting enzyme inhibitors, angiotensin II receptor antagonists and calcium channel blockers can also modify the contribution of apoptosis, independently of the blood pressure fall. The SM22α-DTR mouse may therefore represent a valuable model to study vascular formation and regression in both normal development and disease, such as restriction to flow or hypertension. As reduction in VSMC products in development also produces some forms of congenital heart disease such as supravalvar aortic stenosis (Faury G J Clin Invest. 2003; 112 (9) : 1419-1428) , transgenic animals as described herein may also be a model of specific forms of congenital heart disease. Chronic treatment with DT was also associated with an increase in breaks of elastic laminae, a prelude to aneurysm formation.

Acute arterial injury, such as that occurring at angioplasty or stenting, is followed by rapid induction of medial cell apoptosis, at least in animal models. Thus, in rat or rabbit vessels, balloon overstretch injury results in medial cell apoptosis from 30 minutes - 4 hours after injury (Perlman H et al Circulation.1997;95(4) :981-987; Pollman M et al Circulation. 1997; 96: 1-560; Pollman MJ et al Circ Res. 1999; 84 (1) :113-121) . In pigs, apoptotic cells occur within the media at 6 hours with peaks in the media, adventitia, and neointima at 18 hours, 6 hours, and 7 days after PTCA, respectively (Malik N et al Circulation.1998; 98 (16) : 1657- 1665) . Repair of the vessel after injury is also associated with VSMC apoptosis, both in the media and in the intima, and in the rat occurs 8-21 days after injury (Bochatonpiallat M, et al Am J Path.1995; 146: 1059-1064) . In humans, restenosis after angioplasty has been reported to be associated with either an increase (Isner J et al Circulation 1995; 91:2703- 2711), or decrease (Bauriedel G et al Arterioscler Thromb Vase Biol.1998; 18: 1132-1139) in VSMC apoptosis. Inducing apoptosis in VSMCs also reduces neointima formation after arterial injury, or in vein grafts. Finally, rejection of solid organs is frequently caused by accelerated vascular disease. This process is an accumulation of VSMCs and matrix that ultimately block the vessel. The initial stimulus for VSMC accumulation may be VSMC apoptosis (Moldovan NI et al Angiogenesis 1998 2 (3) : 245-254) . The transgenic animals described herein may therefore be a model of apoptosis after injury or after vein or other graft implantation, and also a model to predict the response to anti-restenosis drugs or drugs to inhibit neointima formation, vein graft disease, or the accelerated vascular disease associated with rejection of transplanted organs .

Tumours require a stable circulation for their growth and metastasis. To provide this circulation, endothelial cells and VSMCs form new vessels (tumour angiogenesis) . Angiogenesis is also implicated in proliferative vascular diseases such as diabetic retinopathy. A stable circulation frequently requires VSMC investment around endothelial cells, to stabilise the endothelial cell tubes and sprouts. Induction of VSMC apoptosis may destabilise these vessels, regressing the tumour or preventing its metastasis. The transgenic animals described herein may therefore provide a valuable model to examine the effects of inducing VSMC apoptosis in angiogenesis, for example as a prelude to drug development for agents that prevent angiogenesis in diseases such as cancer or diabetes.

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Table 1

Claims

Claims :

1. A transgenic non-human animal comprising a heterologous nucleic acid encoding a receptor for an apoptotic agent. wherein said heterologous nucleic acid is expressed specifically in Vascular Smooth Muscle Cells (VSMCs) .

2. A transgenic non-human animal according to claim 1 wherein administration of the apoptotic agent induces apoptosis in VSMCs expressing the heterologous nucleic acid.

3. A transgenic non-human animal according to claim 2 wherein said VSMC apopotosis occurs in the vascular system in the absence of reactive cell division or inflammation

4. A transgenic non-human animal according to any one of claims 1 to 3 wherein the apoptotic agent is diphtheria toxin and the receptor for the apoptotic agent is a diphtheria toxin receptor.

5. A transgenic non-human animal according to claim 4 wherein the diphtheria toxin receptor is the human diphtheria toxin receptor.

6. A transgenic non-human animal according to any one of claims 1 to 5 wherein said heterologous nucleic acid is operably linked to a VSMC specific regulatory element.

7. A transgenic non-human animal according to claim 6 wherein the VSMC specific regulatory element is an SM22α promoter .

8. A transgenic non-human animal according to claim 7 wherein the VSMC specific regulatory element comprises or consists of the nucleotide sequence of residues -445 to +88 relative to the transcriptional start site of the murine SM22α gene sequence.

9. A transgenic non-human animal according to any one of the preceding claims which is a rodent.

10. A transgenic non-human animal according to claim 9 which is a mouse or rat.

11. A transgenic non-human animal according to any one of the preceding claims wherein said non-human animal is a model for a vascular condition.

12. A transgenic non-human animal according to claim 11 wherein the vascular condition is vascular damage or injury.

13. A transgenic non-human animal according to claim 12 wherein the vascular damage is caused by angioplasty, stent implantion, brachytherapy or phototherapy.

14. A transgenic non-human animal according to claim 11 wherein the vascular condition is aneurysm formation, angiogenesis, vasculogenesis, calcification, remodeling, medial atrophy, hypertension or atherosclerosis.

15. A transgenic non-human animal according to any one of claims 1 to 14 wherein the non-human animal has increased susceptibility to atherosclerosis.

16. A transgenic non-human animal according to claim 15 wherein the non-human animal is deficient in apoE and/or LDL receptor.

17. A transgenic non-human animal according to claim 16 wherein the non-human animal comprises a mutation in the apoE gene that abrogates expression or activity.

18. A transgenic non-human animal according to claim 16 wherein the non-human animal comprises a mutation in the LDL receptor gene that abrogates expression or activity.

19. A method of producing a transgenic non-human animal comprising : introducing a heterologous nucleic acid encoding a receptor for an apoptotic agent operably linked to a VSMC specific regulatory element into a non-human animal germ line cell, and; generating a non-human animal from said non-human animal germ line cell.

20. A method according to claim 19 wherein the germ-line cell is an oocyte, egg, or embryonic stem cell.

21. A method according to claim 19 or claim 20 comprising introducing the non-human animal germ line cell comprising the nucleic acid into a blastocyst.

22. A method according to claim 21 comprising implanting the resulting blastocyst into a pseudopregnant non-human animal, wherein said non-human animal gives birth to a chimeric non- human animal.

23. A method according to claim 22 comprising breeding the chimeric non-human animal to produce a transgenic non-human animal comprising the heterologous nucleic acid.

24. A method according to claim 23 comprising crossing the transgenic non-human animal or a descendent thereof which comprises the heterologous nucleic acid, with a non-human animal with increased susceptibility to atherosclerosis to produce offspring with increased susceptibility to atherosclerosis which comprise the heterologous nucleic acid.

25. A method according to claim 24 wherein the non-human animal with increased susceptibility to atherosclerosis is deficient in apoE and/or LDL receptor.

26. A method according to claim 25 wherein the non-human animal comprises a mutation in the apoE gene that abrogates expression or activity.

27. A method according to claim 25 wherein the non-human animal comprises a mutation in the LDL receptor gene that abrogates expression or activity.

28. A method according to claim any one of claims 19 to 27 wherein the transgenic non-human animal is a rodent.

29. A method according to claim 28 wherein the rodent is a rat or mouse .

30. A method of identifying and/or obtaining a compound useful in the treatment of a vascular condition comprising; administering an apoptotic agent to a transgenic non- human animal which specifically expresses a heterologous receptor for the apoptotic agent in Vascular Smooth Muscle Cells (VSMCs) , administering a test compound to said non-human animal, and; determining the effect of said compound on the vascular system of said transgenic non-human animal relative to controls .

31. A method according to claim 30 wherein a reduction in apoptotic effects in the vascular system of said non-human animal in the presence of the compound relative to the absence is indicative that the compound is useful in the treatment of a vascular condition.

32. A method according to claim 30 or claim 31 wherein said vascular condition is vascular damage or injury.

33. A method according to claim 32 wherein the vascular damage is vascular damage caused by angioplasty, stent implantion, brachytherapy or phototherapy.

34 . A method according to claim 30 or claim 31 wherein said vascular condition is aneurysm formation, angiogenesis , vasculogenesis , calcification, remodeling, medial atrophy, hypertension or atherosclerosis .

35 . A method according to any one of claims 30 to 34 comprising identifying a test compound as useful in the treatment of a vascular condition .

36. A method according to any one of claims 30 to 35 wherein the non-human animal is a rodent.

37. A method of identifying and/or obtaining a compound useful in the treatment of atherosclerosis comprising; administering a test compound to a transgenic non-human animal which specifically expresses a heterologous receptor for an apoptotic agent in Vascular Smooth Muscle Cells (VSMCs) , wherein said non-human animal has increased susceptibility to atherosclerosis, administering the apoptotic agent to said non-human animal and. determining the effect of said agent in the presence of the test compound.

38. A method according to claim 37 wherein a reduction in atherosclerosis or associated conditions in the vascular system of said non-human animal in the presence of the compound relative to the absence is indicative that the compound is useful in the treatment of atherosclerosis.

38. A method according to claim 36 or claim 37 wherein the non-human animal is deficient in apoE and/or LDL receptor.

39. A method according to claim 38 wherein the non-human animal comprises a mutation in the apoE gene that abrogates expression or activity.

40. A method according to claim 38 wherein the non-human animal comprises a mutation in the LDL receptor gene that abrogates expression or activity.

41. A method according to any one of claims 37 to 40 wherein the vascular system of said non-human animal comprises atherosclerotic plaques prior to administration of said polypeptide .

42. A method according to claim 41 wherein said non-human animal is fed on a fat rich diet to generate said atherosclerotic plaques.

43. A method according to any one of claims 37 to 42 comprising identifying a test compound as useful in the treatment of atherosclerosis or an associated condition.